This invention relates generally to a heat and pressure fuser for an electrophotographic printing machine, and more particularly the invention is directed to the application of release agent and apparatus therefor.
In a typical electrophotographic printing process, a photoconductive member is charged to a substantially uniform potential so as to sensitize the surface thereof. The charged portion of the photoconductive member is exposed to selectively dissipate the charges thereon in the irradiated areas. This records an electrostatic latent image on the photoconductive member. After the electrostatic latent image is recorded on the photoconductive member, the latent image is developed by bringing a developer material into contact therewith. Generally, the developer material comprises toner particles adhering triboelectrically to carrier granules. The toner particles are attracted from the carrier granules either to a donor roll or to a latent image on the photoconductive member. The toner attracted to a donor roll is then deposited on a latent electrostatic images on a charge retentive surface which is usually a photoreceptor. The toner powder image is then transferred from the photoconductive member to a copy substrate. The toner particles are heated to permanently affix the powder image to the copy substrate.
In order to fix or fuse the toner material onto a support member permanently by heat, it is necessary to elevate the temperature of the toner material to a point at which constituents of the toner material coalesce and become tacky. This action causes the toner to flow to some extent onto the fibers or pores of the support members or otherwise upon the surfaces thereof. Thereafter, as the toner material cools, solidification of the toner material occurs causing the toner material to be bonded firmly to the support member.
One approach to thermal fusing of toner material images onto the supporting substrate has been to pass the substrate with the unfused toner images thereon between a pair of opposed roller members at least one of which is internally heated. During operation of a fusing system of this type, the support member to which the toner images are electrostatically adhered is moved through the nip formed between the rolls with the toner image contacting the heated fuser roll to thereby effect heating of the toner images within the nip. In a Nip Forming Fuser Roll (NFFR) fuser, the heated fuser roll is provided with a layer or layers that are deformable by a harder pressure roll when the two rolls are pressure engaged. The length of the nip determines the dwell time or time that the toner particles remain in contact with the surface of the heated roll. In a Nip Forming Pressure Roll (NFPR) fuser the pressure roll is provided with a deformable outer layer which is deformable by the harder fuser roll.
The heated fuser roll is usually the roll that contacts the toner images on a substrate such as plain paper. In any event, the roll contacting the toner images is usually provided with an abhesive (low surface energy) material for preventing toner offset to the fuser member. Three materials which are commonly used for such purposes are PFA (PerFluoroAlkoxy resin), Viton.TM. and silicone rubber. All of these materials, in order to maintain their abhesive qualities, require release agents specific to the material.
Some RAM systems, specifically those designed for Viton.TM. type fusers, need functional release agents which bond reactively to the fuser roll surface, because non-reactive release agents do not adhere to the low-energy surfaces.
Such functional oils are actually dilute solutions of functional chains (containing groups such as mercapto, amino, etc.) in the conventional non-reactive silicone oil. The functional chains attach to the fuser roll surface by chemical bonds, and the non-reactive chains adhere to the functional chains by much weaker physical (such as van der Waals) chains. Although the functional chains are bonded to the roll, they are eventually removed by the harsh abrasive conditions encountered, and need to be periodically replaced. A certain minimum amount of functional chains (in the order of 0.05 to 0.4 mol %) are required, in order to completely fill the roll surface, without leaving any bare spots which can lead to release failure. Once the roll surface is completely covered with functional chains, only the non-reactive chains need to be replaced continuously as the fuser operates, except for replenishing the few functional chains which are periodically removed from the surface. Therefore in the maintenance mode a far smaller fraction of functional chains is required than in the initial mode.
However, since current RAM systems using functional oils are limited to a single release agent formulation, they are forced to provide the relatively high level (in the order of 0.05-0.4 mol. %) of the functional oils all the time, even in the maintenance mode. The extra functional chains are not bonded to the roll surface because there are no free sites available to them. They are, therefore, passed on to the paper, together with the non-reactive chains. This causes several problems: (1) Cost, because the functional oils are much more expensive than the non-reactive oils; (2) Write-on-copy problems; (3) Stick-on-copy problems, because the functional oils are much more resistant to adhesion than the non-reactive oil and (4) Fuser streaking on OverHead Projector (OHP) transparencies in color copiers/printers in some machines is also attributed to excess functional oil. Number 3 above seems to be related to the functional oils adhering more tenaciously to the paper because of chemical bonding. The stick-on-copy problems are severe enough to jeopardize customer acceptance of certain xerographic imaging machines.
Following is a discussion of prior art, incorporated herein by reference, which may bear on the patentability of the present invention. In addition to possibly having some relevance to the question of patentability, these references, together with the detailed description to follow, may provide a better understanding and appreciation of the present invention.
U.S. Pat. No. 3,934,547 granted to Jelfo et al on Jan. 27, 1976 and U.S. Pat. No. 4,065,585 granted to Jelfo et al on Dec. 27, 1977 disclose a contact fuser assembly for use in an electrostatic reproducing apparatus including an internally heated fuser roll structure comprising a rigid, thermally conductive core which is coated during operation of the assembly with a thin layer of a normally solid thermally stable material with subsequent application of a liquid release agent to the coated core. In the preferred embodiment of the invention the coating material comprises a fluorocarbon telomer such as Vydax 1000 and the liquid release agent comprises a liquid silicone oil.
U.S. Pat. No. 4,214,549 granted to Rabin Moser on Jul. 29, 1980 discloses a heat and pressure roll fusing apparatus for fixing toner images to copy substrates, the toner comprising a thermoplastic resin. The apparatus includes an internally heated, fuser roll cooperating with a backup or pressure roll to form a nip through which the copy substrates pass with the images contacting the heated roll. The heated fuser roll is characterized by an outer layer or surface which by way of example is fabricated from a silicon rubber or Viton.TM. material to which a low viscosity polymeric release fluid is applied. Release fluid is contained in a sump from which it is dispensed by means of a metering roll and a donor roll, the former of which contacts the release fluid in the sump and the latter of which contacts the surface of the heated fuser roll.
U.S. Pat. No. 5,219,612 granted to Patrick J. Finn et al on Jun. 15, 1993 discloses a method of using multilayered member for fusing thermoplastic resin toner images to a substrate in a fuser system of the type wherein a polymeric release agent having functional groups is applied to the surface of the fuser member. The multilayered fuser member has in sequential order a base support member, an adhesive layer comprising a copolymer of vinylidene fluoride and hexafluoropropylene and at least 20% by weight of the adhesive layer of a coupling agent comprising at least one organo functional silane and an activator, a tie coat layer of active ingredients comprising a copolymer of vinylidene fluoride and hexafluoropropylene and an outer elastomeric fusing surface comprising a copolymer of vinylidene fluoride and hexafluoropropylene and containing a metal oxide present in an amount sufficient to interact with a polymeric release agent having functional groups to provide an interfacial barrier layer between said fusing surface and toner.
U.S. Pat. No. 5,217,837 granted to Arnold W. Henry et al on Jun. 8, 1993 discloses a multilayered fuser member for fusing thermoplastic resin toner images to a substrate in a fuser system of the type wherein a polymeric release agent having functional groups is applied to the surface of the fuser member, the fuser member has a base support member, a thermally conductive silicone elastomer layer, an amino silane primer layer, an adhesive layer and a fluoroelastomer surface layer based on the copolymer of vinylidene fluoride and hexafluoropropylene, a metal oxide being present in the fusing surface layer to interact with the polymeric release agent to provide an interfacial barrier layer between the fusing surface and the toner and substantially unreactive with the elastomer.
U.S. Pat. No. 5,017,432 granted to Clifford O. Eddy, on Oct. 29, 1991 relates to a fuser member and fuser system of a type wherein a polymeric release agent having functional groups supplied to the surface of the fuser member has an elastomer fusing surface comprising poly(vinylidenefluoride-hexafluoropropylene-tetrafluoroethylene) wherein the vinylidenefluoride is present in the amount less than 40 mole percent, a metal oxide is present in amounts sufficient to interact with the polymer release agent having functional groups to provide an interfacial barrier layer between the fusing surface and the toner and being substantially unreactive with the elastomer and wherein the elastomer is cured from a solvent solution thereof with a nucleophilic curing agent soluble in the solution and in the presence of less than 4 parts by weight of inorganic base per 100 parts by weight of polymer with the inorganic base being effective to at least partially dehydrofluorinate the vinylidenefluoride.
U.S. Pat. No. 5,531,813 granted Henry, et. al on Jul. 2, 1996 discloses a polyorgano amino functional oil release agent having at least 85% monoamino functionality per active molecule to interacts with the thermally stable FRM hydrofluoroelastomer surface of a fuser member of an electrostatographic apparatus to provide an interfacial barrier layer to the toner and a low surface energy film to release the toner from the surface is introduced herein.
U.S. Pat. No. 5,500,722 granted to Robert M. Jacobs on Mar. 19, 1996 relates to a Release Agent Management (RAM) system for a heat and pressure fuser for fixing black toner images in low and high volume imaging machines and also for fixing color images. An auxiliary oil supply is provided for applying extra oil to an oil impregnated web. The extra oil improves fuser roll release life in every application. Also, enables color fusing which requires higher oil application rates.
U.S. Pat. No. 5,049,944 granted to DeBolt et al on Sept. 17, 1991 discloses an apparatus and method for applying offset preventing liquid to a fuser roll including an oil impregnated web member adapted to be moved by a motor from a supply core to a take up core; and a control to vary the duty cycle operation of the motor to drive the web member at a relatively constant liner speed at a contact nip, the control including a timer to monitor the cumulative time of operation of the motor and to progressively decrease the duty cycle of the motor in response to the cumulative time of operation wherein the progressively decreased duty cycle of operation compensates for the increasing radius of the web member on the take up core to maintain the relatively constant linear speed at the contact nip.